U.S. patent application number 12/934918 was filed with the patent office on 2011-02-03 for system and method for one-trip hole enlargement operations.
Invention is credited to Stefano Mancini, Luk Servaes.
Application Number | 20110024194 12/934918 |
Document ID | / |
Family ID | 41136074 |
Filed Date | 2011-02-03 |
United States Patent
Application |
20110024194 |
Kind Code |
A1 |
Servaes; Luk ; et
al. |
February 3, 2011 |
SYSTEM AND METHOD FOR ONE-TRIP HOLE ENLARGEMENT OPERATIONS
Abstract
A drilling assembly for simultaneous hole enlargement operations
comprises a drill bit, an adjustable diameter reamer, and a hole
opener. The reamer is coupled with, and positioned uphole from the
drill bit. The reamer is adjustable between a first diameter and a
second diameter that is larger than the first diameter. The hole
opener is coupled with, and positioned uphole from the reamer.
Inventors: |
Servaes; Luk; (Lafayette,
LA) ; Mancini; Stefano; (Ravenna, IT) |
Correspondence
Address: |
BAKER BOTTS L.L.P.;PATENT DEPARTMENT
98 SAN JACINTO BLVD., SUITE 1500
AUSTIN
TX
78701-4039
US
|
Family ID: |
41136074 |
Appl. No.: |
12/934918 |
Filed: |
March 27, 2009 |
PCT Filed: |
March 27, 2009 |
PCT NO: |
PCT/US09/38486 |
371 Date: |
September 27, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61040849 |
Mar 31, 2008 |
|
|
|
Current U.S.
Class: |
175/57 ; 175/334;
175/434 |
Current CPC
Class: |
E21B 7/28 20130101; E21B
10/32 20130101 |
Class at
Publication: |
175/57 ; 175/334;
175/434 |
International
Class: |
E21B 7/00 20060101
E21B007/00; E21B 10/28 20060101 E21B010/28; E21B 10/46 20060101
E21B010/46 |
Claims
1. A drilling assembly, comprising: a drill bit; an adjustable
diameter reamer being coupled with, and positioned uphole from the
drill bit, the reamer being adjustable between a first diameter and
a second diameter that is greater than the first diameter; and a
hole opener being coupled with, and positioned uphole from the
reamer; the hole opener including one or more fixed blades and
having a cutting diameter greater than the first diameter of the
reamer and less than the second diameter of the reamer.
2. The drilling assembly of claim 1, wherein the drill bit includes
a drilling diameter that is equal to or larger than the first
diameter of the reamer.
3. The drilling assembly of claim 1, wherein the drill bit includes
a drilling diameter that is smaller than the second diameter of the
reamer.
4. The drilling assembly of claim 3, wherein the second diameter of
the reamer is approximately 50 percent larger than the drilling
diameter.
5. The drilling assembly of claim 1, wherein the second diameter of
the reamer is greater than a diameter of the hole opener.
6. The drilling assembly of claim 1, wherein the reamer comprises a
plurality of movable cutting members, the members being actuatable
from a first position, corresponding to the first diameter of the
reamer, to a second position, corresponding to the second diameter
of the reamer.
7. The drilling assembly of claim 6, wherein the reamer is
configured to allow for actuation of the movable cutting members in
response to a differential pressure.
8. The drilling assembly of claim 1, wherein the hole opener
comprises a fixed blade hole opener including polycrystalline
diamond compact (PDC) cutting elements.
9. The drilling assembly of claim 1, wherein the hole opener and
the reamer are positioned consecutively along a drilling
string.
10. The drilling assembly of claim 1, further comprising at least
one bottom hole assembly element positioned between the drill bit
and the reamer.
11. The drilling assembly of claim 1, further comprising at least
one bottom hole assembly element positioned between the reamer and
the hole opener.
12. The drilling assembly of claim 1, further comprising a
stabilizer positioned uphole from the hole opener.
13. A method, comprising: drilling a borehole through material in a
casing, using a drill bit; actuating an adjustable diameter reamer
that is coupled with and positioned uphole from the drill bit from
a first position having a first diameter to a second position
having a second diameter that is larger than the first diameter;
and enlarging a portion of the borehole adjacent to the bottom of
the casing using a fixed blade hole opener with a diameter greater
than the first diameter and less than the second diameter, wherein
the hole opener is coupled with, and positioned uphole from the
reamer.
14. The method of claim 13, further comprising: passing the reamer,
in the first position, through the casing; actuating the reamer to
the second position after the reamer has passed through the casing;
and enlarging the borehole downhole from the casing using the
reamer.
15. The method of claim 14, further comprising enlarging the
borehole downhole from the casing, using the reamer, to a diameter
that is greater than a diameter of the hole opener.
16. The method of claim 14, further comprising enlarging the
borehole downhole from the casing, using the reamer, by
approximately 50 percent of a drilling diameter of the drill
bit.
17. The method of claim 13, wherein actuating the adjustable
diameter reamer occurs in response to a differential pressure.
18. The method of claim 13, further comprising operating at least
one bottom hole assembly element positioned between the drill bit
and the reamer.
19. The method of claim 13, further comprising operating at least
one bottom hole assembly element positioned between the reamer and
the hole opener.
20. The method of claim 13, further comprising stabilizing one or
more drilling assembly elements located in the borehole using a
stabilizer positioned uphole from the hole opener.
Description
PRIORITY CLAIM
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/040,849 filed Mar. 31, 2008, entitled
System and Method for One-Trip Hole Enlargement Operations, which
is hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates generally to drilling
operations, and more specifically to a system and method for
one-trip hole enlargement operations.
BACKGROUND
[0003] When drilling oil and gas wells, it is frequently desirable
to ream a borehole that has been initially created by a drill bit
or other cutting tool. This reaming can remove any projections that
may have been missed by the first pass of the drilling assembly,
creating a more uniform borehole. In addition, a reamer may be used
to enlarge a borehole (e.g., below a casing shoe), allowing, for
example, the installation of additional casing strings.
[0004] However, since optimum reamers often cannot be used until
they have passed through a first cased section of the borehole,
additional obstructions often remain inside the casing that prevent
or hinder the installation of additional downhole casing strings.
In the past, material in the first casing was removed through the
use of a separate, dedicated drill-out, requiring additional time
and expense. Alternatively, reamers that were less than
optimally-sized for use with a corresponding drill bit were
employed. These approaches may reduce the stability of the drilling
assembly, which may result in more vibrations and drilling
inefficiency.
SUMMARY OF EXAMPLE EMBODIMENTS
[0005] The present disclosure is directed to a system and method
for one-trip hole enlargement operations. The teachings of the
present disclosure allow more efficient operation of drilling
assemblies.
[0006] In accordance with a particular embodiment of the present
disclosure, a system for simultaneous hole enlargement operations
includes a drilling assembly comprising a drill bit. The drilling
assembly further comprises an adjustable diameter reamer that is
coupled with the drill bit and positioned uphole from the drill
bit. The reamer is adjustable between a first diameter and a second
diameter that is greater than the first diameter. The drilling
assembly further comprises a hole opener that is coupled with and
positioned uphole from the reamer. More specifically, the present
invention may also includes a stabilizer positioned uphole from the
hole opener.
[0007] In accordance with another aspect of the present invention,
a method is provided, comprising drilling a borehole through
material in a casing, using a drill bit. The method further
comprises actuating an adjustable diameter reamer from a first
position, having a first diameter, to a second position, having a
second diameter that is larger than the first diameter. The reamer
is coupled with and positioned uphole from the drill bit. The
method further comprises enlarging a portion of the borehole
adjacent to the bottom of the casing using a hole opener, wherein
the hole opener is coupled with and positioned uphole from the
reamer. More specifically, the present invention may also comprise
passing the reamer, in the first position, through the casing. The
invention may further comprise actuating the reamer to the second
position after it has passed through the casing, and then enlarging
the borehole downhole from the casing using the reamer.
[0008] Technical advantages of particular embodiments of the
present disclosure include the ability to run the desired bottom
hole assembly (BHA) tools and enlarge the borehole in a single
pass, without the use of multiple drill strings. Additionally, the
drill bit and BHA tools may be re-used for additional passes, while
the reamer and/or hole opener may be altered or even removed. Thus,
both time and money are saved.
[0009] Further technical advantages of particular embodiments of
the present disclosure include a downhole tool configuration, in
which only two cutting structures are engaged in cutting activities
at the same time, instead of three. More specifically, after the
reamer is activated, only the drill bit and reamer may be engaged
in cutting activities. Therefore, the amount of vibrations and
resulting drill string inefficiencies are reduced. Additional
technical advantages of particular embodiments of the present
disclosure include the use of drill bit that is appropriately sized
for the corresponding reamer, allowing for utilization of
stabilization features of the reamer. This may improve the overall
stability of the drilling assembly, reduce vibration, improve
drilling efficiency, improve logging quality, improve the accuracy
of other BHA tools located along the drill string, and improve cost
efficiency.
[0010] Other technical advantages of the present disclosure will be
readily apparent to one skilled in the art from the following
figures, descriptions, and claims. Moreover, while specific
advantages have been enumerated above, various embodiments may
include all, some, or none of the enumerated advantages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] For a more complete understanding of the present invention
and for further features and advantages thereof, reference is now
made to the following description taken in conjunction with the
accompanying drawings, in which:
[0012] FIG. 1 is a schematic illustration of an oil and gas
drilling rig, including the drilling assembly in accordance with
the present invention;
[0013] FIG. 2A is a partial view of the drilling assembly in
accordance with the present invention;
[0014] FIG. 2B is a partial view of the drilling assembly in
accordance with the present invention;
[0015] FIG. 2C is a partial view of the drilling assembly in
accordance with the present invention;
[0016] FIG. 2D is a partial view of the drilling assembly in
accordance with the present invention;
[0017] FIG. 2E is a partial view of the drilling assembly in
accordance with the present invention;
[0018] FIG. 3 is a schematic view of the reamer in accordance with
the present invention;
[0019] FIG. 4 is a cross-sectional view of the drill bit and reamer
in accordance with the present invention; and
[0020] FIG. 5 is an illustration of a drilling assembly in
accordance with an alternative embodiment of the present
invention.
DETAILED DESCRIPTION
[0021] When drilling oil and gas wells, it is frequently desirable
to use a reamer in conjunction with a drill bit, providing
simultaneous hole enlargement. The reamer can enlarge the borehole,
create a smoother, higher-quality borehole, and extend the life of
the other drill string components. However, when used with a
standard drill bit size associated with the given type of reamer,
excess material, including cement and float collar equipment, is or
may be left behind in the casing of the borehole. This material
needs to be removed to allow for the running of subsequent casing
strings. Therefore, a hole opener may be utilized to remove the
excess material left behind in the first cased section of the
borehole.
[0022] In accordance with the teaching of the present disclosure, a
drilling assembly for simultaneous hole enlargement operations is
disclosed. The object of this disclosure is to allow for the
improved utilization of bottom hole assembly (BHA) elements in
simultaneous hole enlargement operations.
[0023] According to one embodiment of the present disclosure, a
drill bit is provided for drilling a borehole through a formation.
An adjustable diameter reamer is coupled to the drill bit and
positioned uphole from the drill bit. The reamer is adjustable
between a first position having a first diameter and a second
position having a second diameter that is larger than the first
diameter. In operation, the reamer maintains the first position
until it has passed through a cased portion of the borehole. After
passing through, the reamer is then actuated to the second
position, allowing it to enlarge portions of the borehole downhole
from the casing. Additionally, a hole opener is coupled to the
reamer and positioned uphole from the reamer. The hole opener is
used to enlarge the borehole inside a cased portion of the
borehole. According to another embodiment, one or more stabilizers
may also be included in the drilling assembly. The one or more
stabilizer is coupled to and positioned uphole from the hole
opener.
[0024] While the making and using of various embodiments of the
present invention are discussed in detail below, it should be
appreciated that the present invention provides many applicable
inventive concepts which can be embodied in a wide variety of
specific contexts. The specific embodiments discussed herein are
merely illustrative of particular ways to make and use the
invention, and do not delimit the scope of the present
invention.
[0025] FIG. 1 is a schematic illustration of an oil and gas
production operation 10, including a drilling assembly in
accordance with the present invention. A semi-submersible platform
102 is located over a submerged oil and gas formation 12 located
below a sea floor 114. A subsea conduit 110 extends from a deck 104
of the platform 102 to a wellhead installation 112. Platform 102
has a hoisting apparatus 106 and a derrick 108 for raising and
lowering pipe strings such as the work string 100.
[0026] A wellbore 116 extends through various earth strata,
including formation 12. A casing 22 is cemented within wellbore 116
by cement. Work string 100 comprises a drill bit 20, an adjustable
diameter reamer 30, and a hole opener 40. Each of these components
is discussed in more detail below. Additionally, work string 100
may or may not include additional BHA elements. These elements may
include, but are not limited to stabilizers, cross-over subs for
connecting BHA elements, logging while drilling (LWD) components,
measuring while drilling (MWD) components, or rotary steerable
system (RSS) components. These BHA elements may be placed at
various positions along the work string without affecting the hole
enlargement operations of the present disclosure.
[0027] Although FIG. 1 depicts a vertical well, the drilling
assembly of the present invention is equally well-suited for use in
wells having other directional orientations, such as deviated
wells, inclined wells, or horizontal wells. Accordingly, the terms
"downhole" and "uphole" are defined herein to describe locations
away from and toward, respectively, the wellhead installation 112.
In other words, one object which is downhole from another is
farther away from wellhead installation 112 than the other object,
and one object which is uphole from another is closer to the
wellhead installation 112 than the other object. Also, even though
FIG. 1 depicts an offshore operation, the drilling assembly of the
present invention is equally well-suited for use in onshore
operations. Also, even though FIG. 1 depicts one formation and one
production interval, the drilling assembly of the present invention
is equally well-suited for use with any number of formations and
production intervals.
[0028] FIGS. 2A-2E are sequential views illustrating both a
drilling assembly and a method of use in accordance with one
embodiment of the present invention.
[0029] FIG. 2A is a first view of a portion of the drilling
assembly in accordance with the present invention, specifically
drill bit 20 and reamer 30. An adjustable diameter reamer 30 is
coupled to and positioned uphole from the drill bit 20. Reamer 30
is adjustable between a first position having a first diameter and
a second position having a second diameter that is larger than the
first diameter.
[0030] Drill bit 20 is used to drill a borehole through an earthen
formation 28. In the particular embodiment shown, drill bit 20
drills a borehole through material in a casing 22. In other
particular embodiments, a pilot hole may already be drilled through
casing 22, and drill 20 will only drill through the formation below
the casing.
[0031] Drill bit 20 also has a drilling diameter which corresponds
to the diameter of the borehole created by the drill bit. This
drilling diameter will vary depending on the application. Factors
to consider in choosing the appropriate drilling diameter include,
but are not limited to the size of the reamer 30, size of casing
22, or the size of various other BHA elements included on the
drilling assembly. Choosing an appropriate drilling diameter can
have an important impact on performance of the drilling assembly.
For instance, an appropriately-sized drilling diameter may reduce
BHA "whirl" and minimize side forces and bending moments exerted on
the drilling assembly. Additionally, excess vibrations may be
minimized.
[0032] As shown in FIG. 2A, expandable reamer 30 maintains the
first position while passing through casing 22. Similar to drill
bit 20, reamer 30 can be almost any reamer, depending on the
application and results desired. Factors to consider in choosing
the appropriate reamer include but are not limited to the size of
drill bit 20, size of casing 22, desired hole enlargement, and
reamer cutting performance. According to an embodiment of the
present invention, the drilling diameter of drill bit 20 is equal
to or larger than the first diameter of reamer 30, allowing reamer
30 to pass through the borehole drilled by drill bit 20.
Additionally, the drilling diameter of drill bit 20 may be sized
such that excess material 24 remains inside the cased portion 22 of
the borehole. For instance, when a 16'' casing is initially run, an
oil and gas developer may choose to run a 121/4'' drill bit and a
reamer with a first diameter that is equal to or slightly smaller
than 121/4''. Therefore, the drill bit would drill a borehole
having a diameter of 121/4'', and leaving excess material in the
16'' casing. This excess material may include cement or float
collar equipment that is left behind from the installation of
casing 22.
[0033] FIG. 2B is a second view of the drilling assembly in
accordance with the present invention. In particular, drill bit 20
continues to drill the borehole downhole from casing shoe 26 and
into formation 28. Reamer 30 remains in its first position as it
passes through casing 22 of the borehole. Additionally, hole opener
40, coupled to and positioned uphole from reamer 30, is introduced
into contact with formation 28.
[0034] Similar to drill bit 20 and reamer 30, hole opener 40 will
be chosen based on the application and desired results. Factors to
consider in choosing the appropriate hole opener include, but are
not limited to the size of drill bit 20, the size of reamer 30, the
size of casing 22, desired hole enlargement, and hole opener
cutting performance. In one particular embodiment, hole opener is
chosen from a group of hole openers that have fixed blades, as
opposed to adjustable cutting elements found on reamer 30.
Additionally, the cutting elements of hole opener 40 may comprise
polycrystalline diamond compacts (PDC). The selection of a PDC hole
opener may provide for improved strength, performance, and
durability. Many other types of hole openers may be used, including
but not limited to those using roller cones or having adjustable
blades. In particular embodiments, a second reamer may be used in
place of hole opener 40. Alternatively, the functions of reamer 30
and hole opener 40 may be integrated into a single drill string
element operable to provide the same cutting performance as the
reamer-hole opener combination.
[0035] In one embodiment, hole opener 40 has a diameter that is
larger than the first diameter of reamer 30. This allows hole
opener 40 to remove additional material 24 from the cased portion
22 of the borehole, as shown in FIG. 2C. However, as mentioned
above, the size of casing 22 must also be taken into consideration.
Hole opener 40 should remove excess material 24 from within casing
22, but the hole opener should be designed so that it does not
contact or damage the actual casing.
[0036] Other considerations in selecting a hole opener include the
presence of connections that are compatible with other drilling
assembly elements. The presence of connections that are compatible
with elements that are both uphole and downhole from hole opener 40
will reduce the need for extra cross-over sub elements. The
elimination of these elements may reduce vibrations in the drilling
assembly and improve overall life and performance of the drilling
assembly. In one particular embodiment, hole opener 40 is
positioned immediately uphole from reamer 30, with no additional
BHA elements positioned on the drill string between them. This may
be accomplished using traditional cross-over sub elements.
Alternatively, if hole opener 40 has appropriate connections, it
may be attached directly to reamer 30. In one embodiment, this
reamer-hole opener combination is positioned between 90 and 200
feet uphole from drill bit 20. More particularly, the combination
may be positioned between 154 and 200 feet uphole from the drill
bit 20. However, these numbers are indicative of a particular
embodiment, and may vary greatly depending on the actual
application. The spacing of these elements may be chosen to allow
for the inclusion of additional BHA elements between drill bit 20
and reamer 30. Additionally, the spacing may be selected to provide
desired performance and vibration characteristics.
[0037] In FIG. 2D reamer 30 has passed downhole from the casing
shoe 26, and hole opener 40 has removed additional material 24 from
casing 22 of the borehole. At this point, reamer 30 is actuated to
its second position, extending cutting elements 32. Cutting
elements 32 of reamer 30 are used to enlarge the borehole drilled
by the drill bit 20 to a diameter that is larger than the diameter
of hole opener 40.
[0038] As mentioned previously, reamer 30 can be almost any reamer,
depending on the application and results desired. Factors to
consider in choosing the appropriate reamer include but are not
limited to the size of drill bit 20, size of casing 22, desired
hole enlargement, and reamer cutting performance. Reamer 30 may be
selected from various commercially-available adjustable-diameter
reamers, including the HALLIBURTON XR.TM. line of reamers.
According to one embodiment of the current invention, the second
diameter of reamer 30 is larger than the diameter of hole opener
40. Thus, once reamer 30 begins hole enlarging operations, as shown
in FIG. 2E, hole opener 40 effectively becomes "invisible" to the
borehole. This means that the cutting elements of hole opener 40 no
longer touch the walls of the borehole, and drill bit 20 and reamer
30 are left to perform simultaneous drilling and hole enlargement,
respectively.
[0039] For instance, in one particular embodiment, the HALLIBURTON
XR1200.TM. reamer may be used. This particular reamer is capable,
with its first diameter, of passing through a 121/4'' borehole.
When extended to its second diameter, this particular reamer is
capable of enlarging the 121/4'' borehole to a 171/2'' diameter.
Thus, the reamer is too large to operate in its second position
within an original 16'' casing, but is necessary to enlarge
downhole portions of the borehole to prepare for running additional
casing strings.
[0040] FIG. 3 is a more detailed schematic view of the reamer in
accordance with the present invention. As mentioned above, reamer
30 includes a plurality of movable cutting members 32. Cutting
members 32 have a first, contracted position. This contracted
position corresponds to the first diameter of reamer 30. In this
first position, cutting members 32 do not protrude from reamer 30,
and therefore reamer 30 does not provide any hole enlarging
operations. Reamer 30, and in particular cutting members 32, are
actuatable to a second, extended position. This extended position
of cutting members 32 corresponds to the second diameter of reamer
30, and is illustrated by FIG. 3. In this second position, reamer
30 is operable provide hole-enlarging operations.
[0041] The second diameter of reamer 30 may be significantly larger
than the drilling diameter of drill bit 20. In accordance with one
embodiment of the present invention, this second diameter of reamer
30 is approximately 50 percent larger than the drilling diameter of
drill bit 20. Thus, reamer 30 is capable, in certain embodiments,
of enlarging a borehole by approximately 50 percent.
[0042] The cutting elements of reamer 30 may be actuatable to a
second position using various different techniques. In particular
embodiments, this actuation may result from a fluid differential
pressure or an activation drop ball. In alternative embodiments,
electronic or hydraulic means may be used to actuate reamer 30. In
another embodiment, reamer 30 may also be actuated from the second
position with extended cutting elements back to the first position
with contracted cutting members. This may also be accomplished
using varying techniques, including but not limited to a fluid
differential pressure across the reamer or a de-activation drop
ball.
[0043] The cutting elements of reamer 30 may be selected from a
wide range of cutting elements. Factors considered in selecting the
appropriate cutting elements include the desired performance of the
reamer and formation material that the reamer will be operating in.
The material for the cutting elements may include, but is not
limited to polycrystalline diamond compacts, tungsten carbide, or
boron nitride.
[0044] Additionally, reamer 30 includes self-stabilizing features
that include, but are not limited to self-stabilizing element 34.
When reamer 30 is used in conjunction with an appropriately-sized
drill bit 20, this self-stabilizing feature serves to provide
additional stability to the drilling assembly. This added stability
is desirable, as it will reduce side forces and bending moments and
limit lateral movements or deflections of the drilling assembly.
This in turn will result in increased quality of performance by the
drilling assembly, as well as increased drill string life.
[0045] With multiple elements located along the drilling assembly,
care must be taken to minimize problems in the event that one or
more drilling assembly elements fails. One particular type of
problem in this area occurs when drill bit 20 is not in contact
with the bottom of the borehole. If either reamer 30 or hole opener
40 should "stall" while drill bit 20 is in this position, this
could adversely affect any BHA elements located between reamer 30
and drill bit 20 on the drilling assembly. In particular, it is
important to prevent these elements from screwing off from the
resulting torque of a stall. Care should be taken in selecting a
maximum rotary speed for the drilling assembly, which may ensure
that this does not occur. In one particular embodiment of the
present disclosure, a maximum rotary speed of 100 RPM can safely be
applied without accidental BHA spin-off. This value may vary
depending on certain elements, including but not limited to the
inclination of the wellbore and the size and number of drilling
elements.
[0046] FIG. 4 is a cross-sectional view of the drill bit 20 and
reamer 30 in accordance with the present invention. In particular,
this shows the size of the borehole drilled by drill bit 20.
Cutting members 32 of reamer 30 can be seen in their extended
position, providing the second diameter of reamer 30. Thus, reamer
30 is operable to extend the borehole to an enlarged diameter.
[0047] FIG. 5 is an illustration of a drilling assembly in
accordance with an alternative embodiment of the present invention.
In particular, this embodiment of the drilling assembly includes
drill bit 20, reamer 30, hole opener 40, and stabilizer 50.
Stabilizer 50 is coupled with and positioned uphole from hole
opener 40. Stabilizer 50 is used to provide extra stabilization to
the drilling assembly, in addition to that provided by
self-stabilization feature 34 of reamer 30. In the illustrated
embodiment, a single stabilizer is pictured. However, in
alternative embodiments, multiple stabilizers may be employed, or
the stabilizer may be omitted altogether. The inclusion and
placement of one or more stabilizers will depend on the specific
application.
[0048] As with other elements of the drilling assembly, specific
characteristics of stabilizer 50 may be selected from a wide range
of stabilizers to fit a given application. Factors to consider in
choosing an appropriate stabilizer 50 include hole opener size,
reamer size, and the relative position of elements along the
drilling string. In one particular embodiment, stabilizer 50 is
positioned approximately 30 feet uphole from hole opener 40 to
provide optimum stabilization. In other embodiments, this spacing
may vary.
[0049] In addition to stabilization benefits, stabilizer 50 may
provide other benefits. In one particular embodiment, the
stabilizer will provide a "caliper" surface indication that casing
22 has been successfully cleaned out by hole opener 40. This allows
operators at the surface to know that it is safe to run in
additional drilling strings, without any interference from excess
material 24 remaining in casing 22. Additionally, operators may
wish to actuate reamer 30 back to its first position. In this
situation, stabilizer 50 may still provide this caliper
functionality.
[0050] Although the present invention has been described in detail,
it should be understood that various changes, substitutions, and
alterations can be made without departing from the spirit and the
scope of the invention as defined by the appended claims.
* * * * *